[ccache] Why not cache compile failures?

Martin Pool mbp at sourcefrog.net
Sat Sep 29 19:23:22 MDT 2012

I think caching errors would be worth trying.  It may help with
configure, and it may also help with people rebuilding trees that from
time to time have errors in them.

Depending on the compiler, it may be possible to see from the
waitstatus that it was interrupted, and so to avoid caching the
result.  Or, perhaps you can do something with process groups to let
ccache observe the interrupt signal itself and so be sure not to cache

If you emit a message when printing a cached error it ought to be safe
enough to experiment with.

On 29 September 2012 20:07, Shentino <shentino at gmail.com> wrote:
> I'd have to agree that caching failures is tricky.
> Transient errors are temporary by definition and shouldn't be cached.
> What if compile failures were only cached for a limited amount of
> time, say, an hour or so?

I suppose you are proposing this because you think the cache will
often be wrong, and limiting the TTL will limit the damage.  But, if
the cache is unreliable, adding in an additional time-based factor
will make things worse: suppose someone is trying to debug it and
things suddenly start working again?

As much as possible we want things to be pure functions of the input,
both in the input to ccache, and in how ccache itself behaves.

The vast majority of errors are due to actual errors in the source
code in the context of the environment and flags.  If the compiler is
intermittently giving errors for other reasons, the user really needs
to stabilize them before thinking about using ccache.


More information about the ccache mailing list